The partition ratio, D, of In(III) between aqueous chloride/bisuliate solutions of constant ionic strength (5.0) and methylethylketone (MEK) or methylisobutylketone (MIBK) has been investigated radiometrically as a function of chloride/bisulfate ratio and aqueous acidity. Similar experiments were also carried out with aqueous iodide/bisulfate solutions and MIBK. The plot of D versus halide/bisulfate showed a maximum in all cases. The dependence of D on aqueous acidity was found to be linear with MEK, but less than first power with MIBK. Results may be explained by assuming the extraction of all species represented by KtH +. InX m(HSO 4) − 4− m and InX n (HSO 4) 3− n Kt p, where Kt represents a ketone molecule, KtH + a solvated hydroxonium ion, m = 0, 1, 2, 3, or 4, n = 0, 1, 2, or 3 and p = 1, 2 or 3. Formation constants for these complexes have been calculated.